Thermally Actuated Turntable for Conventional/Convection Cooking Ovens

ABSTRACT

The present invention is a thermally actuated turntable suitable for conventional and convection cooking ovens, which posses uneven temperature/cooking characteristics. By means of coupling dissimilar materials, each having a wide variance in their respective coefficients of thermal expansion, the relative linear expansion of these materials caused by the ambient heat found in the cooking chamber of an oven can be utilized in such a way as to create a thermo-linear motor and thus produce relatively small linear displacements of the actuator with relatively high force capabilities. This linear displacement can then be magnified by means of the mechanical advantage of levers to produce sufficient linear displacement of a rack and pinion gear set which is capable of producing multiple rotations of an attached platter during a typical short duration cooking cycle. This slow speed rotational motion is very advantageous for cooking short duration food items.

FIELD OF THE INVENTION

The present invention relates to the field of kitchen appliances and more particularly relates to a thermally actuated turntable used in a conventional or convection cooking oven.

BACKGROUND OF THE INVENTION

Uniform even cooking is the goal and intention of countless kitchen appliances and apparatuses. The recent advent of the convection oven is an attempt to provide a more even distribution of heat in the oven chamber by circulation of the air inside the oven, which facilitates even cooking of the food item.

Because of the inherent uneven cooking characteristics and short cooking times of microwave ovens, by necessity, nearly all microwave ovens are equipped with an integrated turntable which allows the food item to rotate through the “hot” and “cold” spots in the oven. At present however, there are no commercially available turntables for use in conventional cooking ovens. The reason for this is not that conventional ovens don't have uneven heating and cooking characteristics, but more so that a practical and affordable solution for turntables in convection and conventional ovens has not been invented.

Certain food items and specifically those that have short cook time cycles such as breads, cookies and pizzas are much more susceptible to the uneven cooking characteristics of conventional/convection ovens. The area in the back of an oven is typically the hottest part of the oven and the area most likely to produce uneven cooking results. For gas ovens, the sides are generally the hottest parts of the oven.

Because of the high temperatures that exist in conventional ovens and the need to position food items on various rack positions, traditional electric motor driven turntables would be impractical and very costly to produce. Even if the electronics for such turntables were to be located outside the cooking chamber, providing a device that could easily be moved from one rack level to another would be complex and cost prohibitive.

The present invention is a turntable that uses no electric motors, cables, or other external connections and is easily moved from one rack level to another.

SUMMARY OF THE INVENTION

In view of the foregoing challenges inherent in implanting know types of turntables into conventional/convection ovens, this invention provides a solution that was here-to-for not available. As such, the present invention's general purpose is to provide a new and improved turntable concept that utilizes the ambient heat within the oven chamber to heat a thermo-linear motor to actuate a mechanism which spins the turntable platter during a short duration cooking cycle.

To accomplish these objectives a thermo-linear actuator, or series of actuators, created by the combination of materials each with dissimilar coefficients of thermal expansion, work together to produce linear translation. This linear translation is then magnified by a series of linkages and levers to ultimately actuate a rack and pinion gear set which is attached to the shaft of the turntable platter.

Consequently, the change in temperature of the thermo-linear actuators from the room temperature to that of the elevated temperatures within the oven cooking chamber will spin turntable platter and associated food item between three and five times during a typical cooking cycle. By means of opening and closing certain temperature control apertures located on the side of the device, the rate at which the platter will turn can be adjusted.

The more important features of the invention have thus been outlined in order that the more detailed description that follows may be better understood and in order that the present contribution to the art may better be appreciated. Additional features of the invention will be described hereinafter and will form the subject matter of the claims that follow.

Many objects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an outer casing for the invention.

FIG. 2 is an exploded view of a preferred internal mechanism for the invention.

FIG. 3 is a plan view of the internal mechanism of FIG. 2.

FIG. 4 is a plan view, in partial section, of another preferred internal mechanism for the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the drawing, the preferred embodiment of the ThermaSpin is herein described. It should be noted that the articles “a”, “an”, and “the”, as used in this specification, include plural referents unless the content clearly dictates otherwise.

The parts listed are given the reference numerals adjacent their name throughout this specification:

-   1 Frame -   2 First Lever -   3 Parallel crossbar -   4 Second Lever -   5 Rack -   6 Central Pinion Gear -   7 Turntable -   8 Spring -   9 Turntable Support Wheel -   10 Outer Push Tube -   11 Inner Push Rod -   12 Cap -   13 Rod joint 1 -   14 Rod Support -   15 Fixed Pivot Points -   16 Movable Pivot Points -   17 Rocker -   18 Rocker Pivot Point -   19 Pass Through Bore -   20 Second Outer Push Tube -   21 Second Inner Push Rod -   22 Second Cap -   23 Second Rod joint -   24 Second Rod Support -   25 Main Housing -   26 Vent -   27 Bottom Cover

With reference to FIG. 1, the turntable's basic construction comprises a main housing 25, surrounding a turntable platter 7, which provides a rotating surface that is just slightly above that of the main housing 25. The internal structure rotates the turntable 7. One embodiment of the internal structure is shown in FIGS. 2 and 3. A main frame 1, acts as the structural frame of the device and is used to react the loads applied to the device by the weight of food items loaded on the turntable platter 7 and the reaction forces of the actuators and hinge points. In this embodiment, a linear thermo-actuated rod provides the motivating force to rotate the turntable 7. The rod is comprised of an outer tube 10 and an inner rod 11 made of dissimilar materials with different coefficients of thermal expansion (α). In this embodiment, the inner rod 11 has a coefficient of expansion (α₁) that is much smaller than the coefficient of expansion (α₂) of the outer tube 10. They are joined at one end with cap, or nut, 12 and the rod is joined to the linkage system at rod joint 13. As the tube 10 expands with the heat, rod 11 is drawn into the tube 10 and pulls on the linkage system, actuating it. It is of course understood that this is one conception and embodiment of a suitable thermally responsive actuator and others are readily conceivable. Any structure using dissimilar materials with different coefficients of expansion such that a change in temperature may cause a change in the overall shape of the structure may be used. This would include bimaterial disks, strips and springs. The preferred material structure for this embodiment is metal as it is generally resistant to heat and very responsive to heat changes. A highly responsive metal, such as aluminum, cooper or brass is used for the tube 10 while a metal with a low coefficient of expansion, like 64 FeNi (sold under the trade name INVAR) is used for the rod 11. Any combination with vastly dissimilar coefficients of expansion may be used. With the preferred embodiment, INVAR has an az of 1.2 PPM/° C., while aluminum has an α₁ of 24 PPM/° C.

The rod is supported by a fixed rod support 14. The support 14 has a bore through which the rod 11 passes while the tube 10 is anchored on the support, which then provides the fixed point upon which the tube 10 reacts. The thermo-actuated rod in this preferred embodiment is connected to a first lever 2 with a fixed anchor point 15 serving as a fulcrum. As the fulcrum is in close proximity to the rod joint 13, it magnifies the motion of the rod 10 as it is moved by the expanding tube. This first lever 2 is connected to a second lever 4 by a parallel crossbar 3. Like the first lever, it is secured to the frame with a fixed anchor point 15 that also serves as a fulcrum. It also is positioned close to the movable joint 16 to magnify the effect of motion. A rack 5 is then connected to the second lever 4 and interacts with pinion gear 6 to rotate pinion gear 6 and associated turntable 7. Turntable 7 is also supported by a plurality of wheels 9 on the main housing 25. A tension spring 8, keeps the rack gear 5 engaged with the pinion 6 during actuation. This spring loaded non-positive engagement method is important to allow the rack and pinion to “skip” gears in the event that the platter is unintentionally rotated by the user beyond it thermally determined position and at the same time not strip the gears and permanently damage the device.

As second embodiment, shown in FIG. 4, utilizes two actuators of similar structure, where the second actuator comprises a second tube 20 and rod 21, fixed together with a second cap 22. Instead of connecting to the first lever, it connects to a rocker 17 at joint 23 and is secured by fixed anchor 24 to the frame. Both tubes 10, 20 are further stabilized by brace 14 a so as to help maintain relative spatial relation. The first tube 10 is anchored on the rocker 17 instead of a fixed anchor point. The rocker 17 has a fixed anchor 18, about which it rotates and a pass-through bore 19 through which the first rod 11 passes. The combination of the actuators and the rocker further magnifies the mechanical advantage of the levers to move the rack gear 5. Because of the levers 3 and 5, the expansion of the tubes, measured in fractions of millimeters, translates into several centimeters of rack movement and serves to rotate the turntable platter 7 several times over the course of an hour, depending upon ambient temperature and pitch of the rack and pinion gears. The turntable is designed for cooking food items that require less than one hour of total cooking time. Although greater cooking times could conceivably be achieved, they are less practical and the actual need to provide even cooking for an item with a cooking time longer than one hour is much less relevant to the solution provided with this invention.

The main housing may be coupled with a bottom cover 27(FIG. 2) to create an enclosed, thermally isolated system. This can affect the transfer of heat into the system and the eventual expansion of the actuators. Additional thermal insulation may also be provided. A vent 26 (FIG. 1), or plurality of vents, may also be provided to alter the rate at which heat enters the system and thus the rate of rotation.

A number of alternative embodiments are possible. The first alternative embodiment would be to utilize a wind-up spring as the primary actuator. In this configuration, the center of the spring could be attached directly to the turntable platter and potentially produce more total rotations in a cooking cycle. The system would need to be “throttled” to allow the platter to unwind at a controlled rate during the entire cooking cycle.

Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred. 

1. A turntable for conventional and convection ovens, the turntable comprising: a. at least one thermally responsive actuator; b. a linkage system, further comprising at least one lever, operationally connected to the thermally responsive actuator; c. a drive mechanism operationally coupled to the linkage system and further comprising a rack and pinion gear set; and d. a turntable platter coupled to the drive mechanism; wherein the thermally responsive actuator changes shape while exposed to ambient heat within an oven chamber and moves the linkage system and the associated drive mechanism, thereby rotating the turntable platter.
 2. The turntable of claim 1, the at least one thermally responsive actuator comprising at least two different materials with unequal coefficients of thermal expansion.
 3. The turntable of claim 2, the at least one thermally responsive actuator being comprised of an aluminum tube with a coaxial rod of 64FeNi coupled thereto on one end.
 4. The turntable of claim 1, further comprising a covering providing a thermally isolated interior in which the thermally responsive actuator resides.
 5. The turntable of claim 4 the covering further comprising at least one user selectable vent.
 6. The turntable of claim 1, comprising at least two thermally responsive actuators, the actuators being linked in a manner such that their responses to change in ambient temperature co-operate.
 7. The turntable of claim 6, the thermally responsive actuators being comprised of at least two different materials with unequal coefficients of thermal expansion.
 8. The turntable of claim 7, at least one of the thermally responsive actuators being comprised of an aluminum tube with a coaxial rod of 64FeNi coupled thereto on one end. 